A gas turbine is an apparatus that converts thermal energy of high-temperature combustion gas into rotational energy and takes out the converted energy as electric power, and turbine blades incorporated in the gas turbine are always used in the high-temperature combustion gas. Accordingly, the turbine blades each include a cooling flow channel such as a serpentine flow channel, and take in cooling air from the outside to thereby cool a blade body thereof. In particular, a fillet portion forming a joint surface between the blade body and the platform of each turbine blade has a thick wall and thus is difficult to cool. Hence, the wall temperature of the fillet portion is relatively high, and the fillet portion tends to be subjected a thermal stress, in terms of a thermal load and a blade structure. In order to solve this problem, various methods of cooling the fillet portion by convection with cooling air have been proposed as means for cooling the fillet portion of the turbine blade.
Japanese Unexamined Patent Application, Publication No. 2006-112429 discloses the following solution. Cooling air is introduced into a cavity provided in a blade body near a fillet portion, through a cooling flow channel from a base portion (blade root) side, the fillet portion is cooled by convection from the inside thereof, and the cooling air is discharged into combustion gas from a film cooling hole provided in the cavity.
Japanese Unexamined Patent Application, Publication No. 2006-170198 discloses the following solution. A branch pipe for cooling air is drawn from a cooling air supply channel provided in a base portion, a film cooling hole is opened so as to pass through a fillet portion, and the cooling air is blown out from the film cooling hole, to thereby cool the fillet portion.